Optics Question 9
Question: Assertion : A double convex lens (m = 1.5) has focal length 10 cm. When the lens is immersed in water (m = 4/3) its focal length becomes 40 cm. Reason : $ \frac{1}{f}=\frac{{\mu _{l}}-{\mu _{m}}}{{\mu _{m}}}( \frac{1}{R _{1}}-\frac{1}{R _{2}} ) $
[AIIMS 1999]
Options:
A) If both assertion and reason are true and the reason is the correct explanation of the assertion.
B) If both assertion and reason are true but reason is not the correct explanation of the assertion.
C) If assertion is true but reason is false.
D) If the assertion and reason both are false.
E) If assertion is false but reason is true.
Show Answer
Answer:
Correct Answer: A
Solution:
Focal length of lens immersed in water is four times the focal length of lens in air. It means $ f _{w}=4f _{a}=4\times 10=40cm $
